From publisher blurb:
With the forces of the north dominating over all within their sights, only the fiercest of fiery spellcasters can hope to survive their frigid onslaught. Frozen fey, icy outsiders, and other cold creatures make pacts with these wielders of arctic power, so those that oppose them must draw power from the warmth if they are to have any hope of melting these stone cold hearts. This Reign of Winter can only be opposed by an Insurgency of Summer.
Book of Magic: Insurgency of Summer delivers the spells and class options you need to be fully effective against these frigid foes. Inside you will find:
10 new spells,
2 new animal companions,
A new bard masterpiece,
3 new subdomains,
2 new witch patrons,
2 new improved familiars and
A new magic item.